Dear Azzawi

You mean 'top surface ' is the low angle of XRD or the surface of the coating has been polished ?

Personally, I don't think the surface roughness will have a effect on XRD, we use to do powder XRD, and it seems no difference.

Hope my answer will help you

Kind regards

Dear Yu Haojun,

thank you very much for your answer,

the top surface is rough about ~5 micron, and the low angle hide some silicon peaks even the silicon shows less intensity than the powder one, while the back side of the coating layer is more smother its shows the XRD peaks matching with the powder one. iam just wandering for explanation of this phenomenon.

many thanks

Dear Kuznetsova,

the coating layer more than 100 micron so i am pretty sure its not that reason.

many thanks.

I agree with the others, don't think the roughness is the cause. MAybe some segregation of the Al in the surface ?

How do you perfrom the measurement on the other side of the film ? is your substrate thin enough for transmission XRD ?

some other tests you could do:

- use a transmission geometry if possible

- scratch out (remove) the film, make it a powder (mix well) and perfrom again XRD (powder), possible in a capillary and rotate it. Will you find the proper peaks this time ?

Regards, Cristian

Dear Cristian Mocuta,

I pick up the coating layer ~100 micron and did the XRD on other side its gave proper pattern, in somehow the one phase is diminished in the matrix and only in the top surface , also i do agree with others but i still straggling to find good explanation, thank you any way..

Mustafa

It may be such as in a big metallurgical pot: near to the walls the crystal are small or even amorphous and in the middle the grains are large. This occurs because of more intensive heat transfer near to the walls. In the analogical way, the coatings near to interface with substrate have small grains or may be even amorpous and the grains near to the coating's top have big grains. Sometimes, on the top side there is a texture, i.e. a privileged crystallographical growth direction. The effect is thermal and not mechanical.

Dear Prof Pawlowski,

Thank you for your explanation, I do agree there's metallurgical variation. its true i got some amorphous phase in some spots in the matrix, but i have top layer like containing mainly of Aluminum, the idea can be shown in the picture. Is the compressed air concurrent with the torch (Compressed air cleaning) do this phenomenon?

PS: i shall change the words in the question, from "Do roughness of the surface hide some peaks of XRD" to "Are the metallurgical properties changes during high cooling rates in plasma spray coatings!

thank you

Mustafa

Now, to go further we have to know whether Al and Si are mixed and injected with one injector or injected separately with two injectors. In the second case, it is possible that you get in your coating layers of Si, layers of Si and layers of Al+Si. Last thing which comes to my mind is melting and solidification of grains of Al and Si. Have a look on SEM with EDS facility to see the distribution of elements in your coatings. If you do not have EDS, the detector with BSE would be able to see the difference between Si and Al.

Make some more analyses, XRD alone is not enough...

Dear prof. Kuznetsova, thank you very much for your help.

Dear Prof Pawlowski,

I do appreciate your help and i am so lucky to read your comments, actually the Al-Si are alloy, its eutectic 11%wt where previously optimized to get the particles range 20-50 micron, further i did examine the microstructure for the powder particle and i can be sure its have alpha -Al and Beta-Si, and its injected in one nozzle of Gun F4MB-XL, its very confusing of that top surface segregate to that way , however i confirm that by EDS and Raman spectroscopy.

many thanks

Mustafa